The present disclosure relates to the subject matter contained in Japanese Patent Application No.2001-230149 filed on Jul. 30, 2001 and Japanese Patent Application No.2001-366402 filed on November 30, which are incorporated herein by reference in its entirety.
1. Field of the Invention
This invention relates to a magnetic core, a magnetic field shield member, and an electrophotographic apparatus using them and in particular to a magnetic core suitably used for an inductance element such as a coil or a transformer with a magnetic substance installed to produce an electromagnetic characteristic, a magnetic field shield member, and an electrophotographic apparatus using them.
2. Description of the Related Art
A coil or a transformer of an inductance element is one of important parts of electronic machines and electric appliances as a part having inductance. In recent years, electronic machines such as mobile telephones, PHS, and portable computers have tended to be sophisticated, miniaturized, and manufactured at low costs, and high performance, miniaturization, and manufacturing at low costs have also been required for coils and transformers of parts used with the electronic machines.
Most of the size, performance, and cost of a coil or a transformer are determined by a magnetic core used with the coil or the transformer. If a material having large effective magnetic permeability is used as a magnetic core material, the self-inductance and mutual inductance of the coil or the transformer can be increased and parts can be miniaturized. In the coil or the transformer, the loss quantity as represented by the Q value of inductance is a parameter directly involved in the energy efficiency of the coil or the transformer, and the coil or the transformer having a large Q value, namely, a small loss quantity is assumed to be have good performance.
Hitherto, a silicon steel plate and a ferrite sintered compact have been used as magnetic core materials of coils and transformers. Since a metal material such as a silicon steel plate has large conductivity generally, if the metal material is localized in a changing magnetic flux, an eddy current occurs and heat is generated, namely, so-called eddy-current loss occurs. Thus, to use a metal material as a magnetic core, the magnetic core is formed as a structure of stacking several silicon steel plates each formed of thin metal material, thereby preventing the eddy-current loss.
With such silicon steel plate, the loss increases in a high-frequency band. Thus, in the high-frequency band, a ferrite sintered substance of a metal oxide material is used in place of the silicon steel plate.
However, the ferrite sintered substance has the disadvantages that it is not easy to work to any desired shape, that it is also poor in flexibility, and that it is at high cost. Then, use of a composite material comprising ferrite particles dispersed in resin has been proposed. The composite material can be provided as a material which is flexible and is also comparatively small in loss, but has small magnetic permeability and thus is not satisfactory as a magnetic core material.
As the magnetic core of a coil or a transformer, a plurality of portions, such as an E-shaped core and an I-shaped core, may be joined to form one magnetic core. In this case, if only a minute gap exists, it is comparable to the fact that magnetic circuit is largely cut. As the gap exists, the magnetic characteristic of the magnetic core is made worse and a magnetic field leakage occurs, causing an unnecessary electromagnetic field leakage to occur. A coil or a transformer is installed in various electric appliances; in recent years, when designing various electric appliances, it has become necessary to consider the effect of the magnetic flux leaked from such an electric appliance on a human body.
By the way, as image formation technology, electrophotography has become widespread because it provides many merits of high print speed, convenience of eliminating the need for providing a print plate each time, capability of providing images directly from various pieces of image information, comparatively small-sized apparatus, easiness to provide a full-color image, and the like.
An image formation apparatus (electrophotographic apparatus) adopting electrophotography generally forms an electrostatic latent image on the surface of a latent image receptor, brings charged toner into contact with the surface of the latent image receptor to selectively deposite the toner to form a toner image, and transfers the toner image to a record medium via or not via an intermediate transfer body and then fixes the toner on the surface of the record medium by heat and/or pressure, etc., thereby providing an image.
In such an electrophotographic apparatus, usually a fuser comprising a heating roll and a pressurizing roll abutting each other is used for fixing. A record medium on which an unfixed toner image is formed is inserted into a nip part formed by the heating roll and the pressurizing roll abutting each other, whereby the toner is fused by heat and pressure and is fixed on the record medium as a permanent image. A heating member, a pressurizing member shaped like an endless belt may be used in place of the heating roll and/or the pressurizing roll. The heating roll comprises a metal core containing a heat source such as a halogen lamp, the metal core being formed with an elastic layer and a release layer, and the heating roll surface is heated internally by the heat source.
In the fuser, it is desired to instantaneously heat the heating member of the heating roll, etc., and lessen the wait time (warm-up time) as much as possible from the viewpoint of energy saving and the viewpoint of preventing the user from waiting when using the image formation apparatus. However, with the fuser adopting a heating roll containing a heat source such as a halogen lamp, there is a limit to shortening the warm-up time for the reasons that it takes a considerable time in heating the halogen lamp itself, that it takes a time until heat propagates to the surface because heat is generated from the inside of the heating roll, that it takes a time in heating the whole because a heating roll core having a considerable heat capacity must be selected, and the like. If a halogen lamp is used as the heat source, so-called flicker phenomenon occurs in which an energization current flows transiently when the halogen lamp is turned on or off; this is also a problem.
In recent years, as a heating section used in the fuser, section using an electromagnetic induction heating technique has been studied in place of the heat source such as a halogen lamp (JP-A-2000-242108). In the technique, a magnetic field generated by a magnetic field generation section is made to act on a heating member having a conductive layer, whereby the heating member is heated by the electromagnetic induction action; the flicker problem is not involved and only the heated object can be heated instantaneously, so that the warm-up time can be shortened.
The electromagnetic induction heating technique can be applied to any of a roll-shaped member such as a heating roll or a pressurizing roll or a member shaped like an endless belt replacing either or both of the heating roll and the pressurizing roll as the heating member. With the roll-shaped member, only the vicinity of the surface contributing to fixing may be heated and the core need not be heated, so that energy saving can be accomplished. On the other hand, the member shaped like an endless belt is thin and thus has a small heat capacity and can accomplish energy saving of a still higher order.
The electrophotographic apparatus may adopt not only the technique of fixing a record medium to which an unfixed toner image is transferred from a latent image receptor or an intermediate transfer body by a separate fuser as described above (which will be hereinafter simply referred to as xe2x80x9ctransfer and fixing independent techniquexe2x80x9d in some cases), but also a transfer and fixing simultaneous technique of bringing the unfixed toner image formed on an intermediate transfer body into contact with a record medium while heating, and applying pressure, thereby performing transfer and fixing at the same time (JP-A-49-78559, etc.,). In the transfer and fixing simultaneous technique, adopting the electromagnetic induction heating technique in transferring and fixing is also proposed for a similar reason to that in the transfer and fixing independent technique (JP-A-8-76620, JP-A-2000-188177, JP-A-2000-268952, etc.,).
As described above, in the electrophotographic apparatus, adoption of the electromagnetic induction heating technique is examined, but the electromagnetic induction heating technique involves the magnetic field generation section as the main component for heating. Therefore, in the magnetic field generation section in the electrophotographic apparatus, of course, it is also desirable that the eddy-current loss should be suppressed, thereby accomplishing still more energy saving at low cost. In recent years, miniaturization of the electrophotographic apparatus has been underway, and in the electrophotographic apparatus adopting the electromagnetic induction heating technique for fixing or transferring and fixing, it is desirable that the flexibility of the shape of the magnetic core is enhanced to expand the flexibility in designing the apparatus and further the apparatus should be still more miniaturized.
Further, since the electrophotographic apparatus is installed in an office, etc., it is desirable that leakage of a magnetic field from the magnetic field generation section should be prevented so as not to affect various machines installed in the proximity of the electrophotographic apparatus and to protect the human bodies against the effect of a magnetic field. Thus, it is desirable that a member capable of shielding the magnetic field from the magnetic field generation section still more effectively should be adopted as a magnetic field shield member installed in the periphery of the magnetic field generation section.
It is therefore an object of the invention to provide a magnetic core making it possible to set inductance at low cost and easily as the magnetic core is installed in a coil or a transformer and a magnetic field shield member capable of suppress an electromagnetic field leakage efficiently.
It is another object of the invention to provide an electrophotographic apparatus adopting an electromagnetic induction heating technique for fixing or transferring and fixing wherein a magnetic core suppressing an eddy current loss and having high flexibility in shape is used for magnetic field generation section, so that still more energy saving can be accomplished at low cost, the flexibility in designing the apparatus can be expanded, and further the electromagnetic apparatus can be still more miniaturized.
It is still another object of the invention to provide an electrophotographic apparatus adopting an electromagnetic induction heating technique for fixing or transferring and fixing wherein magnetic field leakage from magnetic field generation section can be shielded effectively.
In order to accomplish the objects, in the invention, an aggregate of magnetic particles is used for a magnetic core forming an inductance element such as a coil or a transformer and a part of a magnetic material acting on an inductance element to improve the electromagnetic characteristic of the coil or the transformer and to suppress electromagnetic field leakage.
In particular, a magnetic core of the invention has a magnetic field generation member for supplying magnetic field, a vessel and magnetic particles, in which the magnetic particles form an aggregate and in which the aggregate of the magnetic particles is disposed in the vessel while the magnetic particles are keeping a particle state.
An aggregate of magnetic particles is used as the magnetic material forming the magnetic core and the vessel is filled with the magnetic particles with the particle state of the magnetic particles maintained, so that the shape of the magnetic core can be set as desired and the magnetic core of any desired shape can be easily manufactured simply by selecting the shape of the vessel appropriately.
The magnetic core of the invention adopts the magnetic particles as the magnetic core material and the magnetic particles are maintained intact in the particle state, so that occurrence of the eddy current in the magnetic core can be canceled. Thus, the heat loss of an eddy current can be canceled.
In order to maintain the particle state of the magnetic particles, preferably the shape as the whole of the aggregate of magnetic particles to be used is maintained. Thus, a vessel is used and is filled with magnetic particles, so that the shape as the whole of the aggregate of magnetic particles to be used can be maintained with the particle state maintained.
A magnetic field generation member in which the magnetic core of the invention is disposed may adopt an inductance element such as a coil or a transformer. Most elements for generating a magnetic field are inductance elements such as coils or transformers and the magnetic core is set to any desired shape, thereby making it possible to design the shape of the inductance element as desired.
The magnetic particle includes at least one of iron powder, ferrite powder, and magnetite powder.
The type of magnetic particles is not limited if the magnetic particles can maintain the particle state. If powder of at least iron powder, ferrite powder, or magnetite powder, namely, magnetic particles are adopted in one type or in combination, the characteristic of the magnetic particles can be set as desired.
the vessel has a shape responsive to the temperature characteristic produced by electromagnetism acting on the magnetic particles.
Heat generated by electromagnetism passing through a magnetic material may be used in some cases. For example, it may be used as a heat energy source of a fuser, etc., in an image formation unit. In this case, if characteristic of generated heat, namely, temperature characteristic is contained, preferably the magnetic core of the characteristic matching the temperature characteristic is formed. Then, the shape of magnetic particles is made a shape responsive to the generated temperature characteristic, so that it is made possible to form the magnetic core considering the generated temperature.
The vessel can be made of a nonmagnetic material. The vessel made of a nonmagnetic material is adopted, so that it does not affect the electromagnetic characteristic and the characteristics of the aggregate of magnetic particles with which the vessel is filled and an adjustment element contained in the vessel as required can be optimized to provide any desired magnetic core.
Preferably, the vessel has a lid to allow the magnetic particles to be inserted into and removed from the vessel and the lid seals the vessel.
The vessel is provided with a lid to allow the magnetic particles to be inserted into and removed from the vessel and sealed, so that if the magnetic particles or the vessel is degraded as the magnetic particles or the vessel is used, the magnetic particles and the vessel can be replaced separately and excellent recyclability can be provided.
An adjustment element for adjusting a filling amount of the magnetic particle may be contained in the vessel The magnetic particles are in the particle state and thus can be easily changed in shape. An excessive space may occur depending on the amount of the magnetic particles stored in the vessel. If an adjustment element of a capacity matching the excessive space is contained in the vessel, a vessel having a given capacity can be used and the amount of the magnetic particles stored in the vessel can be adjusted. The shape of the adjustment element is changed, whereby it is made possible to control the magnetic particle distribution in the vessel whenever necessary.
At this time, the adjustment element may be a magnetic substance in a solid state. the adjustment element may also be in a solid state and be made of a nonmagnetic material.
The magnetic core may also be formed of magnetic particles only. However, when a magnetic substance in a solid state having a predetermined characteristic exists, the magnetic particles in the invention may also be used to make adjustment to the magnetic substance.
A magnetic field shield member of the invention is placed in the periphery of magnetic field generation member for generating a magnetic field to shield the magnetic field generated by the magnetic field generation member, the magnetic field shield member made of an aggregate of magnetic particles and filled with the magnetic particles in a vessel with the particle state of the magnetic particles maintained.
The inductance element such as a coil or a transformer may leak a magnetic field to the outside. The magnetic field leaked to the outside changes depending on the shape or the installation point of the inductance element. Thus, the magnetic field shield member is formed of an aggregate of magnetic particles, so that the magnetic field generated by the magnetic field generation member can be shielded efficiently.
Preferably, the magnetic field generation member is a coil or a transformer.
Preferably, the magnetic particles in the magnetic field shield member of the invention includes at least one of iron powder, ferrite powder, and magnetite powder.
Preferably, the vessel has a lid to allow the magnetic particles to be inserted into and removed from the vessel and the lid seals the vessel.
The vessel is provided with a lid to allow the magnetic particles to be inserted into and removed from the vessel and sealed, so that if the magnetic particles or the vessel is degraded as the magnetic particles or the vessel is used, the magnetic particles and the vessel can be replaced separately and excellent recyclability can be provided.
On the other hand, the magnetic core and/or the magnetic field shield member of the invention can be preferably used with an electrophotographic apparatus adopting an electromagnetic induction heating technique for fixing or transferring and fixing. The specific configurations of the electrophotographic apparatus are as follows ((1) and (2)): (1) An electrophotographic apparatus has an image formation unit for forming an unfixed toner image on a surface of a record medium by using electrophotography, a fuser unit having a fixing rotation body and a pressurizing rotation body disposed to press against the fixing rotation body to define a nip part therebetween, and a magnetic field generation member for generating magnetic field, in which the record medium is inserted into the nip part so that a surface of the record medium on which the unfixed toner image is formed contacts with the fixing rotation body, whereby the fuser unit fixes the unfixed toner image on the surface of the record medium, in which a conductive layer is formed in the proximity of the circumferential surface of one of the fixing rotation body and the pressurizing rotation body, and in which the magnetic field generation member is placed close to the one of the fixing rotation body and the pressurizing rotation body.
In this case, the magnetic core of the invention can be preferably used in the magnetic field generation member. To shield at least a part of a leakage magnetic field not affecting the conductive layer, of the magnetic field generated from the magnetic field generation member, preferably the magnetic field shield member of the invention is placed in the periphery of the magnetic field generation member. Of course, preferably the magnetic core of the invention is used in the magnetic field generation member and further the magnetic field shield member of the invention is placed in the periphery of the magnetic field generation member.
As the fixing rotation body and the pressurizing rotation body, a roll-like body and an endless belt body may be selected in any desired combination.
(2) An electrophotographic apparatus has an image support rotation body, an image formation unit for forming an unfixed toner image on a circumferential surface of the image support rotation body by using electrophotography, a heating member disposed in the image support rotation body to abut against the image support rotation body (if necessary), a pressurizing member disposed to face the heating member through the image support rotation body to define a nip part between the pressurizing member and the image support rotation body, and a magnetic field generation member for generating a magnetic field, in which a record medium is inserted into the nip part, whereby the unfixed toner image is transferred and fixed onto a surface of the record medium by heat and pressure, in which a conductive layer is formed at one of a place which is in the proximity of the circumferential surface of the image support rotation body and another place which is in the proximity of an abutment part of the heating member against the image support rotation body, in which when the conductive layer is formed in the image support rotation body is formed, the magnetic field generation member is disposed close to one of the nip part of the image support rotation body and a place on the image support member in the upstream in relation to the nip part, and in which when the conductive layer is formed in the heating member, the magnetic field generation member is disposed close to the heating member.
Also in this case, the magnetic core of the invention can be preferably used in the magnetic field generation member. To shield at least a part of a leakage magnetic field not affecting the conductive layer, of the magnetic field generated from the magnetic field generation member, preferably the magnetic field shield member of the invention is placed in the periphery of the magnetic field generation member. Of course, preferably the magnetic core of the invention is used in the magnetic field generation member and further the magnetic field shield member of the invention is placed in the periphery of the magnetic field generation member.
The image support rotation body may be shaped like a roll or an endless belt.